Ah, Lightroom three. Great program, lots of control over working on your photos.

First off, shoot raw if you can, because JPEG files don't allow much creative control without completely obliterating the original shot.

Try to not mess with your White Balance on the computer that much, it creates awkward lines between colors that look funky in a bad way. Do that on the camera, it looks cleaner and more natural.

Be careful on saturation/vibrance/clarity. Don't go overboard on those, it can make or break a shot.

Just like above, use the fill light and recovery sliders sparingly. They can be helpful when you've got clipped highlights and blacks, but apart from that they give the shot a bland, flat look and can add excess noise.

Learn to use the curves, they can add a pleasing amount of contrast and brightness without going overboard

Apart from that, mess around, play with all the sliders (but not to the extremes) and see what looks good to you. Try some of the built in presets, and make your own that you can go back to for easier access. I've made a few of my own presets, which really saves time going around and setting each individual slider for each picture. I do a little extra work past that though, and I will occasionally do a photo completely by freehand to make it extra shiny. Learn all of it's ins and outs though, and just go exploring and messing around. That's really the best way to learn a program. Read the user's manual too.